This invention is directed to cookware made from a composition containing a select polyarylethersulfone. Also, this invention is directed to a composition suitable for molding into cookware comprising greater than 30 weight percent of the polyarylethersulfone.
Cookware utilized in conventional ovens should have the capability of withstanding the great temperature variations existing between the temperature setting devices and the actual temperatures within the oven. Though the cookware is only exposed to the oven's actual temperature, the user's expectations of the cookware's capacity to withstand heat is a critical factor in the use of that cookware. Putting cookware that deforms at e.g. 200.degree. F. into an oven set for 325.degree. F. is clearly illogical. Equally illogical would be the use of the same cookware in an oven whose temperature setting device fails to accurately control the oven's temperature. Thus a low temperature setting could result in a high oven temperature, and the cookware would still deform. The realities of life are that few commercially available gas and electric ovens have accurate temperature controls and in most cases the ovens run hotter than the temperature setting. In a number of cases, an oven temperature setting of 400.degree. F. resulted in an oven temperature as high as 475.degree.-500.degree. F. This is the basis for the first sentence of this paragraph.
Plastics are typically termed thermoplastic or thermosetting. Thermoplastics are deformable with application of sufficient heat. Because thermosetting plastics (resins) are crosslinked, they are fairly resistent to heat deformation, certainly more so than thermoplatics. Consequently, thermosetting resins have been extensively used for cookware. For example, cookware have been made from melamine-formaldehyde resins, unsaturated polyester resins, and the like. Such plastics have excellent heat resistance. However, they do suffer from a number of significant deficiencies. Because they crosslink during their curing processes when molded, they shrink and pull away from the mold surfaces. Unless they are properly filled with small particulate fillers, the molded objects have very uneven surfaces, and they are subject to significant crazing and/or cracking. High filler loading adversely affects the physical properties of the molded object and precludes the direct obtaining of a glossy surface. Thermosetting resins are difficult to mold. They generally have to be compression or transfer-molded. Such processes require much materials handling, large equipment, complicated and relatively expensive molds, and significant energy costs.
Thermoplastics have been used for coating paper dishware and some of them have been used as cookware. However, their use as cookware is severely restricted, certainly to low temperature or microwave oven applications. Thermoplastics, such as Udel.TM. polysulfone (made by Union Carbide Corporation), have been sold for use in making cookware designed for microwave oven applications. One would expect that some of such cookware has been generally employed in conventional ovens as well. However, Udel.TM. polysulfone has not proven to be suitable for the wide temperatures used in conventional oven cooking and hence, its usage in such applications has not been recommended.
Though the physical properties of a thermoplastic might be considered at first blush the basis for its use as generally employable cookware, i.e., cookware usable in any kind of oven up to a temperature of 500.degree. F., such is clearly not the case. Since cookware is in contact with the food placed therein, the plastic it is made from must be safe to use and not contaminate the food it contacts. Temperature gradients exist within conventional ovens, and cookware is not commonly handled. Such variables require actual working information about a plastic's performance as cookware under a wide variety of conditions. Unless the cookware is intended to be disposable after the first use, it should have the capacity of withstanding repeated washings, by hand or by machine. It should be detergent resistant and not absorb food, oils and fats. It should be able to withstand warping on usage. If it is intended for household use, then it should meet the aesthetics typically favored, such as high gloss and smooth surfaces. It is desirable that the thermoplastic be moldable into a variety of cookware configurations by a simple molding process such as vacuum forming or injection molding. Moreover, since the use conditions are quite severe, necessitating the use of a high performance plastic that tends to be more costly, then all of such performance capabilities are desirably achievable with the minimum amount of plastic usage.
It has been found that a relatively new polyarylethersulfone, possesses these combinations of properties and provides extremely attractive and useful cookware which can be used in essentially all cooking oven applications. Such polyarylethersulfone has been generally described to be useful for circuit board applications (see U.S. patent application Ser. No. 391,422, filed June 23, 1982, commonly assigned). Such polyaryl ethers are more particularly described in European Patent Application Publication No. 0 047 999, published Mar. 24, 1982.